The Linux kernel is the core of every distribution. This chapter
explains how to configure your kernel.
7.42010-07-12Timezone

You first need to select your timezone so that your system knows where it is
located. Look for your timezone in /usr/share/zoneinfo, then copy
it to /etc/localtime. Please avoid the
/usr/share/zoneinfo/Etc/GMT* timezones as their names do not
indicate the expected zones. For instance, GMT-8 is in fact
GMT+8.

The core around which all distributions are built is the Linux kernel. It is the
layer between the user programs and your system hardware. Gentoo provides its
users several possible kernel sources. A full listing with description is
available at the Gentoo Kernel
Guide.

For -based systems we have gentoo-sources
(kernel source patched for extra features).

Choose your kernel source and install it using emerge.

# emerge gentoo-sources

When you take a look in /usr/src you should see a symlink called
linux pointing to your kernel source. In this case, the installed
kernel source points to gentoo-sources-.
Your version may be different, so keep this in mind.

Now it is time to configure and compile your kernel source. You can use
genkernel for this, which will build a generic kernel as used by the
Installation CD. We explain the "manual" configuration first though, as it is
the best way to optimize your environment.

If you want to manually configure your kernel, continue now with Default: Manual Configuration. If you want to use
genkernel you should read Alternative: Using
genkernel instead.

Default: Manual ConfigurationIntroduction

Manually configuring a kernel is often seen as the most difficult procedure a
Linux user ever has to perform. Nothing is less true -- after configuring a
couple of kernels you don't even remember that it was difficult ;)

However, one thing is true: you must know your system when you start
configuring a kernel manually. Most information can be gathered by emerging
pciutils (emerge pciutils) which contains lspci. You will now
be able to use lspci within the chrooted environment. You may safely
ignore any pcilib warnings (like pcilib: cannot open
/sys/bus/pci/devices) that lspci throws out. Alternatively, you can run
lspci from a non-chrooted environment. The results are the same.
You can also run lsmod to see what kernel modules the Installation CD
uses (it might provide you with a nice hint on what to enable).

Now go to your kernel source directory and execute make menuconfig. This
will fire up an ncurses-based configuration menu.

# cd /usr/src/linux
# make menuconfig

You will be greeted with several configuration sections. We'll first list some
options you must activate (otherwise Gentoo will not function, or not function
properly without additional tweaks).

Activating Required Options

Make sure that every driver that is vital to the booting of your system (such as
SCSI controller, ...) is compiled in the kernel and not as a module,
otherwise your system will not be able to boot completely.

We shall then select the exact processor type. The x86_64 kernel maintainer
strongly recommends users enable MCE features so that they are able to be
notified of any hardware problems. On x86_64, these errors are not printed to
dmesg like on other architectures, but to /dev/mcelog. This
requires the app-admin/mcelog package. Make sure you select IA32
Emulation if you want to be able to run 32-bit programs. Gentoo will install a
multilib system (mixed 32-bit/64-bit computing) by default, so you probably
want this option.

Processor type and features --->
(Change according to your system)
(Athlon/Duron/K7) Processor family

Now go to File Systems and select support for the filesystems you use.
Don't compile them as modules, otherwise your Gentoo system will not be
able to mount your partitions. Also select Virtual memory and /proc
file system.

File systems --->
Pseudo Filesystems --->
[*] /proc file system support
[*] Virtual memory file system support (former shm fs)
(Select one or more of the following options as needed by your system)
<*> Reiserfs support
<*> Ext3 journalling file system support
<*> JFS filesystem support
<*> Second extended fs support
<*> XFS filesystem support

If you are using PPPoE to connect to the Internet or you are using a dial-up
modem, you will need the following options in the kernel:

When you've finished configuring the kernel, continue with Compiling and Installing.

Compiling and Installing

Now that your kernel is configured, it is time to compile and install it. Exit
the configuration and start the compilation process:

# make && make modules_install

When the kernel has finished compiling, copy the kernel image to
/boot. Use whatever name you feel is appropriate for your kernel
choice and remember it as you will need it later on when you configure your
bootloader. Remember to replace with the
name and version of your kernel.

# cp arch//boot/bzImage /boot/

Now continue with Kernel Modules.

Alternative: Using genkernel

If you are reading this section, you have chosen to use our genkernel
script to configure your kernel for you.

Now that your kernel source tree is installed, it's now time to compile your
kernel by using our genkernel script to automatically build a kernel for
you. genkernel works by configuring a kernel nearly identically to the
way our Installation CD kernel is configured. This means that when you use
genkernel to build your kernel, your system will generally detect all
your hardware at boot-time, just like our Installation CD does. Because
genkernel doesn't require any manual kernel configuration, it is an ideal
solution for those users who may not be comfortable compiling their own kernels.

Now, let's see how to use genkernel. First, emerge the genkernel ebuild:

# emerge genkernel

Next, copy over the kernel configuration used by the Installation CD to the
location where genkernel looks for the default kernel configuration:

Now, compile your kernel sources by running genkernel all. Be aware
though, as genkernel compiles a kernel that supports almost all
hardware, this compilation will take quite a while to finish!

Note that, if your boot partition doesn't use ext2 or ext3 as filesystem you
might need to manually configure your kernel using genkernel --menuconfig
all and add support for your filesystem in the kernel (i.e.
not as a module). Users of EVMS2 or LVM2 will probably want to add
--evms2 or --lvm2 as argument as well.

# genkernel all

Once genkernel completes, a kernel, full set of modules and
initial root disk (initrd) will be created. We will use the kernel
and initrd when configuring a boot loader later in this document. Write
down the names of the kernel and initrd as you will need it when writing
the bootloader configuration file. The initrd will be started immediately after
booting to perform hardware autodetection (just like on the Installation CD)
before your "real" system starts up.